[FTS] with RBAC attempting op you don't have permission for logs you out

With RBAC enabled, many operations may result in HTTP 401 because the user has limited permissions.

This has the effect of logging you out. (appears to be browser behavior)

This creates a really bad user experience for FTS because we don't customize the UI to only show valid options. For example, if you try to create index on bucket you don't have permission for, you get logged out with no explanation.